Egyptian forces on Friday launched air strikes on six jihadist training camps in Libya in retaliation for an attack on Coptic Christians in Egypt in which at least 29 people were killed, many of them children.

Assailants in three pick-up trucks attacked the bus on Friday as it was heading for the Saint Samuel monastery in Minya province, more than 200 kilometres (120 miles) from Cairo, before fleeing, the interior ministry said.

State television reported six air strikes against "terror camps in Libya", specifying that jihadist training camps were hit in the eastern Libyan city of Derna. Witnesses there reported four strikes by a single aircraft.

"Egypt will not hesitate in striking terror camps anywhere, either inside (the country) or outside it," Sisi said.

A spokesman for the pro-Al-Qaeda Majlis Mujahedeen Derna, which controls the city, said the Egyptian air force carried out eight raids on the city without causing casualties.

Addressing US President Donald Trump, Sisi said: "You have said that your priority is to confront terrorism, and I trust you are capable of doing that."

In a statement released in Washington, Trump said: "The bloodletting of Christians must end, and all who aid their killers must be punished."

"Terrorists are engaged in a war against civilisation, and it is up to all who value life to confront and defeat this evil."

No group has yet claimed responsibility for attacking the bus.

Footage on state television showed the bus riddled with bullet holes, while cellphone footage and pictures on media sites showed victims lying in the desert sand.

International condemnation

State television quoted a health ministry official as saying a "large number" of the victims were children.

"They used automatic weapons," Minya governor Essam el-Bedawi told state television of the attackers.

Official sources said that the attack, which prompted widespread international condemnation, killed 29 people.

It came after jihadists had threatened more strikes against the Copts, who make up about 10 percent of Egypt's 90-million population.

The north Minya town of Maghagha saw scenes of anger and despair on Friday.